1. Field of the Invention
The present invention relates to an illumination system. More particularly, the present invention relates to a dual lamp illumination system.
2. Description of Related Art
Referring to FIG. 1, a conventional dual lamp illumination system 100 is used for a projection apparatus. The dual lamp illumination system 100 includes a first lamp 110, a second lamp 120, a prism 130, and a light integration rod 140. The first lamp 110 is capable of emitting a first beam 112. The second lamp 120 is capable of emitting a second beam 122. The first lamp 110 and the second lamp 120 are disposed to face each other. The prism 130 is disposed between the first lamp 110 and the second lamp 120, and has a first reflective surface 132 and a second reflective surface 134 to reflect the first beam 112 and the second beam 122 to the light integration rod 140, respectively.
The dual lamp illumination system 100 has two lamps 110 and 120, the first beam 112 and the second beam 122 enter the light integration rod 140 at the same time, and thus the dual lamp illumination system 100 provides a higher level of illumination. Furthermore, chief rays of the first beam 112 and the second beam 122 are obliquely incident to the light integration rod 140 respectively in two symmetric directions, and thus the brightness distribution of illumination output by the dual lamp illumination system 100 is uniform. However, when one of the first lamp 110 and the second lamp 120 is powered off or damaged, only one of the first beam 112 and the second beam 122 is obliquely incident to the light integration rod 140 (only one chief ray is obliquely incident in one direction), and thus the brightness distribution of the illumination output by the dual lamp illumination system 100 is ununiform. Thus, the brightness of image projected by the projection apparatus is distributed ununiformly.
Referring to FIG. 2, a dual lamp illumination system 200 disclosed in U.S. Pat. No. 6,196,699 includes a first lamp 210, a second lamp 220, and a prism 230. The first lamp 210 and the second lamp 220 are disposed to face each other, and respectively emit a first beam 216 and a second beam 226. The prism 230 is disposed between the first lamp 210 and the second lamp 220, and has a first reflective surface 232 and a second reflective surface 234. A part of the first beam 216 emitted by the first lamp 210 is reflected by the first reflective surface 232. The other part of the first beam 216 is projected onto a lamp reflector 224 of the second lamp 220, then reflected by the lamp reflector 224, passes through a lampwick 222 of the second lamp 220, reflected by the lamp reflector 224 and reflected by the second reflective surface 234 sequentially. A part of the second beam 226 emitted by the second lamp 220 is reflected by the second reflective surface 234, and coincides with the first beam 216 reflected by the second reflective surface 234. The other part of the second beam 226 is reflected by a lamp reflector 214 of the first lamp 210, passes through the lampwick 212 of the first lamp 210, reflected by the lamp reflector 214 and reflected by the first reflective surface 232 sequentially, thereby coinciding with the first beam 216 reflected by the first reflective surface 232.
In the dual lamp illumination system 200, as the first beam 216 coincides with the second beam 226 after being reflected by the prism 230, when one of the first lamp 210 and the second lamp 220 is powered off, the brightness of the illumination output by the dual lamp illumination system 200 is reduced to a half, but the brightness distribution is still uniform. However, in the dual lamp illumination system 200, external beams pass through the lampwick 212 and the lampwick 214 concentratively. Specifically, a part of the first beam 216 passes through the lampwick 222 of the second lamp 220 concentratively, and a part of the second beam 226 passes through the lampwick 212 of the first lamp 210 concentratively. Therefore, the lifespan of the lampwick 212 and the lampwick 222 is reduced significantly.